On DESI's DR2 exclusion of $\Lambda$CDM

Abstract

The DESI collaboration, combining their Baryon Acoustic Oscillation (BAO) data with cosmic microwave background (CMB) anisotropy and supernovae data, have found significant indication against the $\Lambda$CDM cosmology. This can also be interpreted as the significance of the detection of the $w_a$ parameter that measures variation of the dark energy equation of state. DESI's DR2 article quotes exclusion of $\Lambda$CDM for combinations of BAO and CMB data with each of three different and overlapping supernovae compilations (at 2.8-sigma for Pantheon+, 3.8-sigma for Union3, and 4.2-sigma for DESY5). We show that one can neither choose amongst nor average over these three different significances. We demonstrate how a principled statistical combination yields a combined exclusion significance of 3.1-sigma. Further we argue that, faced with these competing significances, the most secure inference from the DESI DR2 results is the 3.1-sigma level exclusion of $\Lambda$CDM obtained from combining DESI+CMB alone, omitting supernovae.

arXiv comment6 pages with two figures, updated to match version accepted by MNRAS

References in corpus (28)

• Observational Evidence from Supernovae for an Accelerating Universe and a Cosmological Constant
• Measurements of Omega and Lambda from 42 High-Redshift Supernovae
• A Phantom Menace? Cosmological consequences of a dark energy component with super-negative equation of state
• Exploring the Expansion History of the Universe
• Accelerating Universes with Scaling Dark Matter
• The Pantheon+ Analysis: Cosmological Constraints
• DESI 2024 VI: Cosmological Constraints from the Measurements of Baryon Acoustic Oscillations
• The Pantheon+ Analysis: The Full Dataset and Light-Curve Release
• SALT2: using distant supernovae to improve the use of Type Ia supernovae as distance indicators
• DESI DR2 Results II: Measurements of Baryon Acoustic Oscillations and Cosmological Constraints
• Probing the dark energy: methods and strategies
• The Atacama Cosmology Telescope: DR6 Gravitational Lensing Map and Cosmological Parameters
• Planck intermediate results. LVII. Joint Planck LFI and HFI data processing
• DESI 2024: Reconstructing Dark Energy using Crossing Statistics with DESI DR1 BAO data
• SALT3: An Improved Type Ia Supernova Model for Measuring Cosmic Distances
• Interpreting DESI's evidence for evolving dark energy
• Combining cosmological datasets: hyperparameters and Bayesian evidence
• Interpreting DESI 2024 BAO: late-time dynamical dark energy or a local effect?
• Underdetermination of dark energy
• UNITY: Confronting Supernova Cosmology's Statistical and Systematic Uncertainties in a Unified Bayesian Framework
• Dynamical Dark Energy in light of the DESI DR2 Baryonic Acoustic Oscillations Measurements
• The DESI DR1/DR2 evidence for dynamical dark energy is biased by low-redshift supernovae
• SALT2 Versus SALT3: Updated Model Surfaces and Their Impacts on Type Ia Supernova Cosmology
• Power Spectra to 1% Accuracy between Dynamical Dark Energy Cosmologies
• Bayesian Model Averaging in Astrophysics: A Review
• Improved null tests of $\Lambda$CDM and FLRW in light of DESI DR2
• On dataset tensions and signatures of new cosmological physics
• Talk about Pivots

Cited by in corpus (10)

• Is Dark Energy Dynamical in the DESI Era? A Critical Review
• Cosmological constraints on Galileon dark energy with broken shift symmetry
• Calibration-independent consistency test of DESI DR2 BAO and SNIa
• Probing departures from $\Lambda$CDM by late-time datasets
• Evidence for evolving dark energy from DESI DR2 BAO and Pantheon${}^{+}$, DES-Dovekie, and Union3
• Model-Independent Dark Energy Measurements from DESI DR2 and Planck 2015 Data
• Comparing measures of the Hubble and BAO tensions in $\Lambda$CDM and possible solutions in $f(Q)$ gravity
• Lowering the Horizon on Dark Energy: A Late-Time Response to Early Solutions for the Hubble Tension
• Breaking Free from the Swampland of Impossible Universes through the DESI Portal
• Diverse reddening distributions in sight lines to type Ia supernovae